1. Field of the Invention
The present invention relates to a device and method for holding a component in a fixed position on a shaft. Particularly, the present invention is directed to a device and method for holding a split seal component on a rotatable shaft, and a pusher seal assembly including the same.
2. Description of Related Art
There are many situations in which a component of machinery must be mounted in a fixed position on a shaft. For example, a variety of machines include a rotating shaft that must be sealed around the shaft circumference to prevent the leakage of fluids. Typically, a seal assembly including two opposing sealing rings having corresponding sealing faces is used to seal the annular gap between the rotating shaft and the machinery housing. One sealing ring is referred to as the non-rotating sealing ring because it is mounted on a stationary structure adjacent the rotating shaft, while the other is referred to as the rotating sealing ring because it is secured to the rotating shaft so as to rotate with the shaft.
In a conventional seal assembly, each of the various seal components, including the non-rotating sealing ring and the rotating sealing ring, are generally fabricated as solid, single-piece members. Since the rotating sealing ring must be secured around the circumference of the shaft, mounting is performed by either disassembling the machinery or sliding the solid ring-shaped component along the length of the shaft. However, both methods considerably increase the time required for assembly, as well as the risk of damage to the machinery and the shaft. Once in position, the rotating sealing ring is typically mounted on the shaft using an adaptor, which is slid into position and then secured by set screws against movement in the axial and circumferential direction relative to the shaft.
Split seals have been developed so that each solid, single-piece component of the conventional seal assembly is replaced with a plurality of mating portions configured to surround the shaft when assembled. Specifically, each component of the split seal is formed by two halves, each subtending 180.degree. around the periphery of the shaft. Each half has two opposite ends that mate with the ends of the corresponding half of the split component. Assembly and replacement of the seal components therefore can be accomplished without requiring disassembly of the machinery or relative movement along the length of the shaft. Rather, each split seal component is simply assembled around the shaft. In this manner, there are typical applications in which replacement of a solid seal assembly could take eight to twenty-four hours, while replacement of a split seal assembly might take one hour.
To minimize leakage across the split seal assembly, the rotating sealing ring and adaptor of the split seal should directly contact the shaft. Manufacturing limitations typically require, however, that a diametrical gap of at least about 0.002 to 0.005 inches be provided between the outer surface of the rotating shaft and the inner surface of the rotating sealing ring and adaptor. Therefore, these split seal components cannot be mounted in a fixed position on the shaft by simply mating the ends of the split adaptor halves together. This is because the diametrical gap precludes the transfer of sufficient resistant forces or torque to secure the rotating sealing ring or the adaptor to the shaft and against relative movement in the axial and circumferential directions. However, if the shaft diameter is made greater than that of the inner surface of the ring and adaptor, the ends of the adaptor halves will not butt together, allowing leakage therebetween.
One method that has been developed for mounting a split sealing ring adaptor to a shaft includes reducing the length of each half of the adaptor so that a gap of 0.005 to 0.02 inches between the ends of the adaptor halves is created. When the adaptor halves fare attached together, this gap allows the inside surface of the adaptor to be brought into engagement with the outer surface of the shaft. A separate sealing member, such as rubber or a similar elastomeric member, is used to seal the gap that is created between the ends of the adaptor halves. However, the risk and amount of leakage across the split seal assembly is generally increased when such elastomeric materials are used in this manner. Sealing in the axial direction is also accomplished by positioning elastomeric members, such as conventional O-rings between the adaptor and the shaft.
Another method that has been used is to secure the adaptor halves to the shaft, both axially and tangentially, with set screws. Each set screw extends radially inwardly through an adaptor half to contact the shaft. In such an arrangement, the inside diameter of the adaptor should be 0.002 to 0.005 in. greater than the outside diameter of the shaft. A disadvantage of this method is that the actual clamping force of the set screw on the shaft is dependent on the operator's strength. If too little force is used, the adaptor will slide on the shaft. If too much force is used, the halves may separate from each other to the extent that the elastomeric members between the halves, and between the halves and the shaft, can not properly fill the gaps between the two halves and between the halves and the shaft, thereby leading to leakage. Furthermore, the set screws may mar the shaft at the point of contact.
Therefore, there remains a need for a device and method for holding a component, particularly a split seal component, on a shaft in a fixed position.
With regard to the non-rotating sealing ring, a limited amount of axial movement is anticipated in split seal assemblies known as pusher seals. Specifically, the pusher seal assembly is configured to allow hydraulic pressure to urge the non-rotating sealing ring toward the rotating ring during operation. A spring is also provided to urge the rotating and non-rotating sealing rings into sealing engagement when operating pressure forces are not sufficient. Hence, the non-rotating sealing ring is retained against movement in the circumferential direction, yet allowed to move in the axial direction.
Assembly of the components of the split seal assembly may be difficult since a great deal of manipulation of components may be required. Further, the sealing rings are often split by cracking a solid sealing ring to form two or more portions having irregular mating surfaces. Although relatively fine grained material lacks the interlocking characteristic of a coarser material, coarser material is often more difficult to handle without damaging the radially extending mating surfaces.